It is often desired to track and identify items, such as packages, containers, etc., and to communicate information concerning such items wirelessly. One method of tracking and providing information concerning packages is to attach a wireless communication device, such as a radio frequency identification (RFID) transponder or other identification device, to packages. The information communicated concerning the packages may include expiration dates, “born on” dates, lot numbers, manufacturing information, and the like. A wireless communication device may be attached to an individual package or to a container containing multiple packages.
A problem exists when a wireless communication device is attached to packaging or containers constructed out of a conductive material such as foil. A pole antenna connected to the wireless communication device will not radiate properly if the wireless communication device is attached on the outside of the package. The pole antenna will be shielded if the wireless communication device is placed inside the package.
It may be advantageous for such a wireless communication device to communicate on different frequencies so that one device can be used for various applications. For instance, an operating frequency of 2.45 GHz is used frequently outside the United States, but an operating frequency of 915 MHz is frequently used in the United States. Many companies manufacture wireless communication devices that are capable of operating at both 915 MHz and 2.45 GHz frequencies so that either frequency can be chosen for operation. However, wireless communications device applications, such as attaching wireless communication devices to packages for informative and tracking purposes, configure the device to communicate on only one frequency—either a frequency for the United States or a frequency for use abroad. It would be advantageous to construct a wireless communication device with an antenna structure that is capable of communicating at more than one frequency. This would allow one wireless communication device to be applicable for uses in both the United States and abroad.
In addition to conductive materials, wireless communication devices are also used with many other substrates. Each substrate has its own dielectric characteristics, which typically affect the impedance matching between the wireless communication device and its antenna. Impedance matching ensures the most efficient energy transfer between an antenna and the wireless communication device.
Further, there are occasions when it may be desirable to change the impedance of the antenna to achieve better impedance matching between the antenna and the wireless communication electronics. While many techniques are known, other techniques, such as those in the present invention, are not and have not been applied to a wireless communication device. Thus, there is a need to provide a variety of techniques to achieve the desired impedance matching so that there are more opportunities available to a designer, such as choice of geometry, size, or the like, to achieve the desired operating frequency without compromising the performance of the wireless communication device.